Refrigerated storage or warehouse facilities are commonly used within the food industry to prevent bacteria and prolong the life of perishable foods. To reduce energy costs, these refrigerated warehouses typically have one or more cold storage rooms adjacent to rooms at more moderate temperatures. Doorways allow access between these rooms by forklifts and personnel. At open doorways between cool and warm areas, some of the higher pressure, but lighter, warm moist air will flow into the cool area primarily from the top of the doorway (warm air infiltration) in exchange for heavier cool air at the bottom of the doorway (cold air exfiltration). Such air flow has maximum and opposite forces at the top and bottom of the doorway which diminish to zero near the midpoint of the doorway.
Depending upon the conditions of the two air masses, this cold air exfiltration and warm air infiltration can cause numerous problems. Infiltrating humid warm air tends to become supersaturated within the cold room, which leads to precipitation or airborne ice crystals at the doorway. The infiltrating humid warm air also leads to ice build-up within the cold room, especially on the floor, doors, walls and/or products adjacent to the doorway. Ice can also build up within refrigeration coils causing damage to the refrigeration unit. Additionally, the warm air infiltration inflates energy costs for refrigerating the cold rooms. Conversely, the exfiltrating cool air tends to mix with the humid warm air to cause fog at the warmer side of the doorway. The fog reduces visibility and can lead to wet slippery floors at the doorway.
There have been many attempts in the prior art to reduce or eliminate the adverse effects of the colliding cool and warm air masses at the doorways of cold storage rooms. One common approach is to use a physical barrier at the doorway, including ordinary hinged doors having overlapping edges or sweeps that reduce the air flow through the gaps around the door panels. Hinged doors hamper the ingress and egress through the doorway, and the sealed edges have been found problematic because during periods of non-use ice tends to form on the seal and the floor or door jamb freezing the doorway closed. Another type of physical barrier is the well-known strip door often having transparent plastic or vinyl strips depending from the doorway header. Strip doors are typically low-cost and improve passage through the doorway, but the strips can separate with use allowing cross-filtration of the air. Once this begins to occur, the strips can become coated with ice so as to reduce visibility through the doorway and potentially join the strips together. Also, strips doors are typically unsuitable for storage of items requiring sanitary conditions, such as cold food storage, since the strips may come in contact with the items when passing through the doorway.
Another solution to this problem has been achieved with the use of what is commonly referred to as an “air curtain”. An air curtain eliminates physical barriers at the doorway and facilitates unobstructed passage through the doorway. An air curtain is formed by an apparatus having an air mover producing a relatively high velocity air stream across the doorway, either from side to side or top to bottom, to counteract the forces of the infiltrating air masses. The air curtain apparatus may also contain a heater to condition the air stream flowing through it and reduce or prevent fogging or precipitation at the doorway, which may otherwise have occurred as the air stream mixes with the warm and cool air masses while passing across the doorway.
A problem that must be addressed by an air curtain doorway is mixing of the air that is intended to form the curtain with the warm side air and with the cold side air. The width of these doorways can be considerable, for example ten feet or more, and ideally all of the air that is blown out of the supply side of the doorway, and no other air, is sucked into the return side of the doorway for recirculation through the doorway. Sucking in the warm moist air can result in the formation of ice, which requires running the heaters to keep ice from forming, and sucking in the cold air also forms ice, which requires running the heaters, and creates an additional load for the refrigerated room refrigeration system. Running the heaters, of course, results in energy inefficiency and increased costs.
The typical solutions in the prior art have been to increase the volume of air flow across the doorway, run multiple airflows, or simply run the heaters more. The present invention addresses this problem to minimize the mixing of warm side and cold side air with the air curtain stream.